1. Field of the Invention
The invention relates to control levers and, more particularly, relates to control levers which can be deflected into contact with a switch such as a deadman's switch to actuate the switch.
2. Description of the Related Art
Switches are used in a wide variety of industrial applications to operate devices or to prevent the operation of such devices. Many of these switches require prolonged actuation or actuation by a user who for one reason or another has part of his or her attention distracted from operation of the switch.
Typical of these switches are so-called "deadman's" switches which are provided on industrial devices such as cranes, backhoes, tractors, cherry pickers, and many other applications in which large and/or potentially dangerous equipment is operated under electrical, pneumatic, or hydraulic power. Such switches are designed to prevent movement of the control device when the operator's attention is distracted from such a device. These switches typically permit operation of the device only when they are depressed and otherwise prevent the transmission of electrical, pneumatic, or hydraulic power to valves and other devices required to operate the machine.
The typical deadman's switch comprises a simple push-button switch which is spring biased into its open position and which must be depressed into its actuated or closed position permitting operation of the device on which it is mounted. The typical switch is very small--about one-quarter of an inch in diameter--and is thus difficult to locate when the operator is not viewing the switch and is difficult to depress for extended periods of time because the user's finger or thumb becomes tired and slips off from the switch. In either event, power to the device being manipulated is unintentionally interrupted, thus leading to an inconvenient or possibly even dangerous situation.
One proposal to alleviate this problem contemplates the replacement of the small push-button switch with a larger push-button switch or so-called "mushroom" switch which requires less accurate positioning of the operator's hand. However, these switches still require relatively accurate placement of the user's thumb or forefinger and thus only partially alleviate the problems discussed above and also are very susceptible to damage and breakage.
Another proposed device designed to facilitate the actuation of a deadman's switch employs a control lever which is connected to the device on which the switch is mounted and which extends over the switch by a substantial distance and which may thus be more easily actuated. One such control lever is disclosed in U.S. Pat. No. 4,270,032, which issued to Dobberpuhl on May 26, 1981. The lever disclosed by this patent is designed for use with a deadman's switch which prevents a snow blower from operating unless the switch is depressed. The control lever is connected to the handle bar of the snowblower via a pivot pin extending transversely through the handle bar and into opposed lateral sides of the control lever. A stop pin extends out of the handle bar and into an elongated slot formed in the control lever. A return spring is provided between the handle bar and the control lever between the pivot pin and the free longitudinal end of the control lever.
The device is operated by deflecting the control lever against the biasing force of the return spring into contact with the deadman's switch, thus depressing and closing the switch and permitting operation of the machine. When the operator's hand is removed from the lever, the lever is returned to its initial position under the biasing force of the return spring, thus opening the switch and deactivating the snowblower. Movement of the control lever in both directions is limited by the return stop.
Control levers of the type discussed immediately above exhibit several disadvantages.
First, the pivot connection of the lever to the device on which it is mounted is relatively complex and is susceptible to breakage. More specifically, such pivot connections require that holes be provided in both the control lever and the device in which the lever is mounted and that a pin be inserted through or at least into the device on which the lever is mounted. Such an arrangement is particularly undesirable where delicate wires or other breakable members extend through the device on which the lever is mounted and are thus susceptible to damage during connection or disconnection of the lever to or from the device on which it is mounted. This problem may be alleviated by the replacement of the pin with an external hinge. Such a hinge, however, still requires relatively complex assembling steps.
The typical control lever of the type discussed above is also susceptible to breakage through excessive forces being imposed on the lever in any number of directions. While this problem is alleviated somewhat by the provision of the stop in the device discussed above, it cannot prevent water from seeping into the pivot connection between the lever and the device on which it is mounted and thus cannot prevent freezing and expansion of such water which could damage or destroy the connection. The problem of water damage exists whether the connection of the control lever to the device on which the switch is mounted comprises pivots, hinges, or any other such fastener permitting movement of the lever relative to the device on which it is mounted.
Another disadvantage resides in the fact that the return spring may become stuck, thus preventing actuation of the lever towards the switch, or may be broken, thus failing to assure separation of the lever from the switch when the lever is not depressed.
Still another disadvantage resides in the fact that the typical lever is made out of a rigid material such as metal. Such a lever typically has a higher spring rate than the associated switch. Accordingly, an operator may lodge an object in between the switch and the lever, thus defeating the purpose of the switch. A metallic lever may also be uncomfortable to the touch, especially when temperatures are below freezing such that the user's skin may actually freeze fast to the lever.